NONO Protein Regulates the Immune Response in Human Triple-Negative Breast Cancer Cells

Breast cancer (BC) remains a leading cause of cancer-related mortality worldwide, with limited treatment options for triple-negative breast cancer (TNBC). The RNA-binding protein non-POU domain-containing octamer-binding protein (NONO) has emerged as a critical regulator of tumorigenesis, but its role in immune signaling remains unexplored. We analyzed the effect of NONO protein by modulating its expression using short hairpin RNA (shRNA) and a chemical inhibitor (R)-SKBG-1. We demonstrate that NONO depletion in MDA-MB-231 TNBC cells leads to cytoplasmic DNA accumulation, micronuclei formation, and activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS/STING) pathway, resulting in enhanced modulation of the immune response. NONO-deficient cells showed increased cGAS and STING activation, Tank-binding kinase 1 (TBK1) phosphorylation, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) nuclear localization, and transcription of pro-inflammatory genes such as CC Motif Chemokine Ligand 5 (<i>CCL5</i>). These effects were recapitulated by pharmacological inhibition using (R)-SKBG-1, confirming NONO's immunosuppressive function. Our findings establish NONO as a key modulator of immune activation in TNBC and suggest that its inhibition may enhance anti-tumor immunity. This work paves the way for potential combination strategies involving NONO inhibitors and immune checkpoint blockade, particularly in tumors with homologous recombination deficiencies or limited immune infiltration.